Repeater circuits



March 24, 1925,,

- J. B. MORRlLL REPEATER CIRCUITS Filed Nov'. 6', 1920 Patented Mar. 24,1925.

mm "STATES JOSEPH'B. MORRILL, OF ST. LOUIS, MISSOURI, ASSIGNOR TOWESTERN ELECTRIC COM- PAN'Y, INCORPORATED, OF NEW YORK, N. Y.,-ACORPORATION OF NEW YORK.

REPEATER CIRGU ITS.

Application filed November 6, 1920. Serial No. 422,199.

To all /10/22. it may concern:

Be it known that I, JOSEPH B. MonnILL, a citizen of the United States,residing at St. Louis. in' the county of St. Louis and State ofMissouri, have invented certain new and-useful Improvements in RepeaterCircuits, of which the following is a full, clear. concise, and exactdescription.

This invention relates to electric circuits,

especially repeatingsystems, and an object of thein'vention is to reducedistortion of waves transmitted by such systems.

As is well known in the art. weak currents or signals may be amplifiedto any des red degree by impressing them on one or more vacuum tubeamplifiers arranged to work into each other by suitable circuitconnections. In employing the vacuum tube as an amplifier, it has beenfound that .the tube works most efficiently when the impedance betweenthe control electrode and the oathode is composed substantially ofresistance with no capacity component. In that form ofa vacuum tubewherein the control electrode or grid is within the tube and adjacent tothe cathode, there is present a oer.- tain amount of capacity betweenthe cathode and the grid, dependent in value upon the size of theelectrodes and the distance there between. This capacity effect isgenerally negligibly small for currents of low frequency, but if thefrequencies impressed on the tube are relatively high the capacity offeet may be quite appreciable and cause a certain amount of distortionin the current waves to be repeated. J I

In accordance with this invention, the undesired grid-cathode capacitymay be substantially neutralized by including ina shunt path to the gridand cathode. a high resistance and an inductance, the inductance havingsuch a valve as to tune with the grid capacity for the frequency or bandof frequencies which are of the most importance in the impressedcurrents. The high resistance element preferably employed in connectionwith the inductance element serves to broaden the tuning of the circuitincluding the grid capacity and the inductance elementwhereby uniformtransmission is secured over a wider range of frequencies.

This invention will be better understood bv reference to the followingdetailed de- "tube amplifier having a cathode G, a' control or gridelectrode 7. and an anode 8. Heat ing current for cathode 6 is suppliedby a battery 9. space current for the tube is supplied from a source ofvoltage 10. The input electrodes-6 and 7 of the tube. are connected toan incoming line 11, 11 by means of a transformer 12. The outputelectrodes 8 and 6 of the tube. are connected to the outgoing line 13,13, by means of the trans former t4. \Yith such an arrangement, tube 5is adapted to impress upon outgoing line 13, 13, amplified currentreceived from incoming line 11, 11. I

It has been found even Where the fre quency of the incon'iing current isas low as 1,000 cycles, that the impedance between grid '7 and cathode 6consists not only of a resistance component but has an appreciablecapacity component. This capacity component produces distortion in therepeated signals and is. therefore, undesirable particularly for ultraaudio frequencies where the effect is most marked. In accordance withthis invention, this undesired grid capacity is substantiallyneutralized or effectively eliminated by inserting, in a path in shuntto the grid and cathode, an inductance 15 and a high resistance 16, theinductance; 15 being of such a value as to be resonant with thegrid-cathode capacity for th frequency of the incoming currents fromline 11. 11. In case the incoming currents are of a plurality offrequencies. resonance should occur for that frequency or band offrequencies which is of the most importance. Resistance element 16serves to broaden the tuning of the circuit including the grid capacityand inductancolfi. thereby neutralizing the grid capacity over a widerrange of frequencies than would occur in the case where only aninductance element was employed. The insertion of resistance 16 andinductance 15 in the input circuit of repcater 5 has, therefore, beenfound to improve, to a considerable degree, the quality of thetransmission between lines 11 and 13. The value the resistance element16 should have depends, to a certain extent, upon the value of theeffective resistance and capacity between the input electrodes of thetube associated therewith. The higher the effective resistance betweenthe grid and cathode, the smaller the value of resistance'16 in order toproduce the desired effect. In one case,

for example, it was found that resistance 16 should be of the order ofhalf a me ohm,

' in the case where the grid and catho e effective leakage resistancewas approximately 3 megohms, and the effective capacity was 30 micromicrofarads.

s As an example of the value inductance I may have, it was found thatwith a vacuum tube having an effective capacity of micro microfarads andeffective leakage resistance' of '3 megohms between. its inputelectrodes for a frequency of QOQO cycles. inductance 15 shouldbeapproximately 20 henrys. H 1

What is claimed is:

1. In combination, an amplifying device having an impedance comprising aresistance component and a reactance component,

an input circuit for said device, and means comprising a resistance anda reactance associated with said input circuit for substan tiallyannulling said reactance component.

2., In combination, a vacuum tube, a trans lating device having an inputcircuit, the

internal impedance ofsaid tube with respect,

to the currents impressed on said input cir' cuit comprising aresistance component and a capacity component, and apath comprisinganlnductance and a resistance associated With sa dunput circuitforsubstantially annulling said capacity component for the frequency ofthe impressed currents.

3. In combination, a vacuum tube'having an anode, a cathode and acontrol electrode,

- the impedance'between said control electrode component and a capacitycomponent, means com onent and a ca acit com onent an i111.

' from said line, and means for substantially and said cathodecomprising a resistance for impressing current variations on saidcontrol electrode and means for substantiah ly annulling the capacitycomponent between the two electrodes for the frequency of'the currentsimpressed thhreon, said means comprising an inductance and a resistance.4:. In combination, a-vacuum tube having an anode, a cathode and acontrol electrode, the impedance between said control electrode and saidcathode comprising a resistance coming line, a transformer forimpressing on said control electrode current variations annulling saidcapacity component for the frequency of the currents impressed thereon,

.said tube.

said means comprising a resistance and an inductance effectively inshunt to said line.

5. The combination ofan incoming line, a vacuum tube amplifierforrepeatin'g with-. out distortion, having an anode, a cathode and a.controlelectrode, a transformer between said line and said amplifier, apath in shunt'to said control electrode and said cath- .ode withrespect. to said transformer, said path\compr1s1ng a res stance and aninductance, the value of said lnduct'ance being dependent upon theinternal characteristics of 6. In combination, a vacuum tube having ananode, a cathode and a control electrode,

the impedance between said control electrode and said cathode comprisinga resistance component "and a capacity component, means for impressingcurrent variations on T said control.electrode, a shunt path to saidcontrol electrode and'said cathode comprising a resistance and aninductance, said inductance being of such a'value as to resonate withsaid capacity forthe frequency of said current variations, saidresistance having a value of the order of one half, a megohm.

7. In combination, a vacuum tube having an anode, a cathode and acontrol electrode,

and a path in shunt to said line of inductive reactance and highresistance forsubstantially annulling said reactance component.

9. In combination, an electron discharge device having. an anode, avcathode, and a control electrode, a circuit comprising a transformer,means connecting said cathode and said control electrode across saidcir-' cuit, and a path connected across said circuit and comprising aresistance and an inance being dependent upon the internalcharacteristics of said tube.

In witness whereof, I hereunto subscribe. my name this 1st day ofNovember A. 1)., 1920.

its

ductance in series, the value of said induct- JOSEPH MORRILL.

